Books like Magic at the Gate

Allie Beckstrom's lover, Zayvion Jones, is a Guardian of the Gate, imbued with both light and dark magic and responsible for ensuring that those energies don't mix. But Zayvion lies in a coma, his soul trapped in death's realm. And when Allie discovers that the only way to save Zayvion is to sacrifice her very own magical essence, she makes a decision that may have grave consequences for the entire world.